Kaposi's sarcoma-associated herpesvirus virion-induced transcription activation of the ORF50 immediate-early promoter.

Lytic cycle reactivation of Kaposi's sarcoma-associated herpesvirus (KSHV) can be initiated by transcription activation of the ORF50 immediate-early (IE) gene promoter (ORF50p). We provide evidence that KSHV virions stimulate transcription of ORF50p. Virion activation was resistant to UV inactivation and cycloheximide treatment. The virion-responsive element was mapped to core promoter region -150 to + 1 relative to the ORF50 initiation codon. Electrophoretic mobility shift assays and chromatin immunoprecipitation suggest that KSHV virions indirectly alter the protein composition and chromatin modifications at ORF50p. These data suggest that KSHV virions possess an IE trans-inducing function similar to that observed in alpha- and betaherpesviruses.